(color online) (a) Schematic diagram of aluminum/silica wavelength-scale square cavity laser. (b) SEM image of fabricated square cavity laser with a side length of about 2.2 μm, with the inset showing a tilted view of the cavity. (c) Room temperature lasing spectra for the square cavity laser. (d) Output peak power and linewidth of the lasing mode versus incident peak pump power for the square cavity laser, with the inset showing the detailed lasing spectrum. (b) Theoretical curves and the experimental results of laser mode power against input pump power. Reproduced from Ref. [62].